Wireless subsea monitoring and control system

ABSTRACT

A method for monitoring a subsea hydrocarbon production or processing apparatus involves mounting a subsea control module (SCM) on or adjacent the apparatus, mounting a first base unit on or adjacent the apparatus at a distance from the SCM, mounting a plurality of first sensor devices on the apparatus, each of the plurality of first sensor devices being configured to generate a first sensor signal representative of a condition of a component of the apparatus or a property of a fluid in the apparatus, operating each first sensor device to generate a corresponding first sensor signal, wirelessly transmitting each first sensor signal from its corresponding first sensor device to the first base unit, wirelessly receiving the first sensor signals at the first base unit, transmitting the first sensor signals from the first base unit to the SCM, and receiving the first sensor signals at the SCM. In this manner, the SCM is provided with a plurality of first sensor signals which are representative of a condition of each of a number of first components of the apparatus and/or a property of a fluid at each of a number of first locations in the apparatus.

This application is a continuation of U.S. patent application Ser. No.13/138,801 filed on Dec. 21, 2011, which is a national stage filing ofInternational Patent Application No. PCT/US2010/000989 filed on Mar. 31,2010, which is based upon and claims priority from U.S. ProvisionalPatent Application No. 61/211,641 filed on Apr. 1, 2009.

The present invention relates to a system for monitoring and controllingsubsea hydrocarbon production and processing systems. More particularly,the invention relates to a monitoring and control system which includesa multitude of wireless sensors for monitoring various operatingconditions of a subsea production or processing system. The sensorsgenerate signals relating to the operating conditions and transmit thesesignals to a local wireless base unit using, for example, radiofrequency communication. The wireless base unit in turn communicates thesensor data to an adjacent subsea control module, which generatescommand signals for controlling various components of the subseaproduction or processing system based upon the sensor data or relays thesensor data to a surface-based monitoring and control station forfurther processing.

BACKGROUND OF THE INVENTION

Subsea production systems typically include a christmas tree or similarapparatus which is mounted at the upper end of a well bore that extendsinto a subterranean hydrocarbon-bearing formation. The principalfunction of the christmas tree is to provide an interface between thewell and the external environment for regulating the flow of productionfluid from the well and for facilitating intervention on the well ordownhole systems during the operational life of the well. Accordingly,christmas trees commonly include a number of flow control valves andassociated actuators for controlling the flow of production fluid fromthe well, as well as multiple sensors for monitoring certain operatingconditions of the production system, such as the state of the valves andactuators and the properties of the production fluid.

Similarly, subsea processing systems usually comprise flow controlvalves and associated actuators for regulating the flow of productionfluid through a processing apparatus. In addition, these systemscommonly employ a number of sensors for monitoring certain operatingconditions of the system, such as the state of the various components ofthe apparatus and the properties of the production fluid.

The various components of subsea production and processing systems arecontrolled and/or monitored by a subsea control module (SCM) which inturn is monitored and/or controlled by a remote monitoring and controlstation. The SCM is normally located on or adjacent the subseaproduction or processing apparatus, and the monitoring and controlstation is typically located on a surface vessel or platform or at aremote land-based facility. The SCM is usually connected to themonitoring and control station through an umbilical. The umbilical mayinclude hydraulic lines for supplying hydraulic fluid to varioushydraulic actuators located on he subsea production or processingapparatus. The umbilical may also include electric and/or fiber opticlines for supplying electrical power to certain components of theproduction and processing system and for communicating control signalsand data between the monitoring and control station and the SCM.

Conventional subsea production and processing systems incorporate arelatively small number of sensors to measure the operating conditionsof the system. In order to maximize production efficiency it isnecessary to optimize the functioning of the subsea production orprocessing system. A key component in such optimization is the effectivemonitoring of the system using a range of sensors. To do thiseffectively requires employing far more sensors on the system than areconventionally used.

In addition to the sensors, means for relaying the sensor outputs to theSCM are also required. The sensors on subsea production and processingsystems are conventionally hardwired to the SCM using electrical oroptical fiber cabling. The requirement for such cabling and theirconnections into the sensors and the SCM constitute a significant costand technical challenge. Further, when the number of sensors is greatlyincreased, the cabling and connections become a major limitation.Moreover, employing a large number of sensors and associated cablingunder the insulation layer on, for example, a christmas tree isrestricted by the potential for the cables to damage or degrade theinsulation.

Conventionally acoustic techniques have been employed for underwaterwireless communication. However, such systems have low data capacity andare limited by background noise and noise from subsea devices. Inaddition, acoustic communications are adversely affected by ambientconditions, such as temperature gradients and air bubbles. Acousticsystems are thus not a viable option for wirelessly connecting multiplesensors to an SCM in a subsea production or processing system.

Thus, there exists a need for an efficient and effective means forwirelessly connecting numerous sensors on a subsea production orprocessing apparatus to an SCM to enable the SCM and/or a remotemonitoring and control station to monitor the operating conditions ofthe production or processing system and control various components ofthe system.

SUMMARY OF THE INVENTION

In accordance with the present invention, these limitations in the priorart are addressed by providing a subsea system for producing orprocessing a hydrocarbon production fluid with a plurality of sensors,each of which generates a sensor signal that is representative of acondition of a component of the system or a property of a fluid; a baseunit which mounted on or adjacent the system and is in wirelesscommunication with each of the sensors; and a subsea control modulewhich is in communication with the base unit. In operation, the sensorsignals are transmitted wirelessly from the sensors to the base unit andare then transmitted from the base unit to the subsea control module.

The sensor signals may be transmitted from the sensors to the base unitusing, for example, radio frequency signals, magnetic signals, oroptical signals. In addition, the sensor signals may be digitallymodulated.

In accordance with one embodiment of the invention, the base unit ismounted apart from the subsea control module.

In accordance with another embodiment of the invention, the base unitcomprises a memory in which a plurality of the sensor signals are storedprior to being transmitted to the subsea control module.

In accordance with a further embodiment of the invention, each sensorcomprises or is connected to a corresponding wireless receiver. Inaddition, each sensor may comprise a memory in which its correspondingsensor signal is stored prior to being transmitted to the base unit.Furthermore, each sensor may transmit its corresponding sensor signal tothe base unit in response to a command signal received from the baseunit. Moreover, the base unit may comprise a memory in which a pluralityof the sensor signals are stored prior to being transmitted to thesubsea control module.

In accordance with yet another embodiment of the invention, each sensorcomprises a corresponding local power supply. In addition, the powersupply may be replenishable. For example, each of a plurality of thesensors may comprise a Seebeck device for replenishing the power supply.

In accordance with still another embodiment of the invention, the subseasystem comprises a second base unit which is mounted on or adjacent thesystem and is in communication with the subsea control module. In thisembodiment, each of the base units is in wireless communication withcorresponding ones of the plurality of sensors.

Thus, the present invention uses wireless systems to access a multitudeof sensors deployed on subsea production or processing systems.According to the invention, a wireless base station is located on thesubsea system and multiple wireless sensors are placed at relevantlocations on, e.g., a christmas tree or subsea processing apparatus.Preferably, the wireless communication is achieved using radiofrequency. Although radio frequencies are heavily attenuated in water,the short ranges required for the on-system communications involved inthe present invention are achievable using such frequencies. Thewireless communications may also be effected using magnetic or opticalsignals.

The resultant reduction in cost and cabling requirements allows far moresensors to be deployed on the subsea apparatus. The use of a multitudeof sensors enhances the quality and utility of the data obtained andprovides the basis for enhanced operation of the subsea system.

These and other objects and advantages of the present invention will bemade apparent from the following detailed description, with reference tothe accompanying drawings. In the drawings, the same reference numbersmay be used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the wireless subsea monitoringand control system of the present invention shown in conjunction with anexemplary subsea christmas tree; and

FIG. 1A is an enlarged view of the portion of the christmas treedesignated “1A” in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The wireless subsea monitoring and control system of the presentinvention utilizes wireless sensors and sensor networks to overcome thepractical and cost imposed limitations of conventional hardwiredmonitoring and control systems when incorporating many more sensors thanis conventionally utilized. The ability to incorporate many more sensorsgreatly enhances the effectiveness of real-time hydrocarbon productionmanagement. In addition, the increased data obtained from the sensorsmay be used with conventional condition performance monitoringtechniques to provide enhanced assessment of system performance andstatus, which can subsequently be utilized for planned maintenance andfailure prediction.

Although the wireless subsea monitoring and control system of thepresent invention is applicable to a variety of subsea production andprocessing systems, for purposes of brevity it will be describedhereafter in the context of an exemplary subsea christmas tree.

Referring to FIG. 1, the wireless subsea control and monitoring systemof the present invention, which is indicated generally by referencenumber 10, is shown installed on an exemplary christmas tree 12. Thechristmas tree 12 is mounted on a wellhead 14 which is positioned at theupper end of a well bore (not shown). The wellhead 14 supports a tubinghanger 16 which is connected to the upper end of a tubing string 18 thatextends through the well bore to a subterranean hydrocarbon formation.

The christmas tree 12 includes an axial production bore 20 whichcommunicates with the tubing string 18 and a vertical annulus bore 22which communicates with the tubing annulus. The production bore 20 isconnected to a production outlet 24 through which the production fluidis conveyed during normal operation of the christmas tree 12.

The christmas tree also includes a number of production bore valves 26for controlling flow through the production bore 20, a number ofproduction outlet valves 28 for controlling flow through the productionoutlet 24, and a number of annulus valves 30 for controlling flowthrough the annulus bore 22. During operation of the christmas tree 12,production fluid is diverted by the upper production bore valve 26 intothe production outlet 24, through a choke 32 and out a productionflowline 34 which may lead, for example, to a subsea processing system.

The valves 26, 28, 30 and the choke 32 are each actuated by acorresponding hydraulic or electric actuator. The hydraulic actuatorsare supplied by one or more accumulators 36, which in turn are connectedto an external source of hydraulic fluid. The accumulators 36 may alsosupply a number of hydraulically actuated connectors, such as a treeconnector 38 which secures the christmas tree 12 to the wellhead 14 anda flowline connector 40 which connects the production outlet to theproduction flowline 34.

In accordance with the present invention, numerous sensors are providedfor monitoring the operating conditions of various components of thechristmas tree 12 and the properties of the production fluid. Forexample, a number of position sensors 42 may be provided for monitoringthe open or closed state of the valves 26, 28, 30, a position sensor 44may be provided for monitoring the position of the choke 32, and anumber of position sensors 46 may be provided for monitoring the latchedor unlatched state of the connectors 38, 40. In addition, suitablesensors 48 may be provided for measuring the voltage or current of theelectrical actuators associated with certain valves.

The properties of the production fluid may be monitored with a number ofpressure and temperature sensors 50, 52 located at various points in theproduction bore 20 and the production outlet 24. Similarly, a number ofpressure and temperature sensors 54, 56 may be provided to measure thepressure and temperature of the fluid in the tubing annulus and thetubing bore. In addition, pressure sensors 58 may be provided formeasuring the pressure of the hydraulic fluid in the accumulators 36,and a number of erosion detectors 60 and a vibration detectors 62 may beprovided to measure the wear and vibration of certain components of thechristmas tree 12, such as the production flowline 34.

The christmas tree 12 may also include a number of leak detectors 64 fordetecting leakage past various seals and valves, and one or more ROVposition sensors 66 for sensing the presence of an ROV at acorresponding docking station 68.

In accordance with the present invention, the wireless subsea controland monitoring system 10 includes as wireless transmitter/receiver baseunit 70 which is ideally mounted on or adjacent the christmas tree 12.The base unit 70 communicates wirelessly with the sensors, preferablyusing radio frequency signals. Accordingly, the base unit 70 is locatedwithin a suitably short range of the sensors to ensure that the radiofrequency signals are not overly attenuated in the surrounding water.

The base unit 70 transmits the received sensor data to a conventionalSCM 72. The SCM 72 is configured in a conventional manner to enable itto monitor the operating conditions of the christmas tree 12, includingthe properties of the production fluid, and control certain componentsof the christmas tree based on the sensor data. The SCM 72 may alsocommunicate the sensor data to a remote monitoring and control station74. In the exemplary embodiment of the invention shown in FIG. 1, themonitoring and control station 74 is located on a surface vessel 76 andis connected to the SCM 72 through an umbilical 78. Like the SCM 72, themonitoring and control station 74 monitors the operating conditions ofthe christmas tree 12 and generates signals for controlling certaincomponents of the christmas tree. These controls signals arecommunicated to the SCM 72, which then controls the components asinstructed.

Also, the sensors may comprise wireless receivers, and the base unit 70may be configured to wirelessly transmit control signals to the sensors.For example, the sensors may be provided with memory to store theirassociated data and then transmit the data upon receipt of anappropriate signal from the base unit 70. Furthermore, the base unit 70may relay the sensor data in real time to the SCM 72 or may be providedwith means to store the sensor data for subsequent relay to the controlmodule.

The sensors may be conventional devices which are selected depending onthe parameters which are desired to be detected. In addition, thesensors ideally include communications electronics for converting thesensor data into signals which can be transmitted wirelessly and fortransmitting the sensor data to the base unit 70. Alternatively, one ormore of the sensors may be conventional devices which in turn areconnected to a wireless transceiver. An example of such a wirelessenabled sensor is shown in FIG. 1A. In this example, a conventionalpressure sensor 80 is hard-wired to a wireless transmitter 82. Thetransceiver 82 receives the data from the sensor 80, converts it into aformat capable of being transmitted wirelessly, and then transmits thedata signal to the base unit 70.

The sensors and the base unit 70 may be configured to communicate usingany suitable communication scheme, such as that disclosed in WO2008/109929 A1, which is hereby incorporated herein by reference. Inaddition, the sensors may be powered with batteries or capacitors thatare replenished using conventional power scavenging techniques, such asvibration, thermal, light or wireless signals. One suitable energyscavenging technique which employs a Seebeck device is disclosed in WO2008/109929 A1.

A range of wireless sensors may be employed to measure the relevantoperating conditions of the christmas tree and the production fluid,such as pressure, temperature, flow, vibration, corrosion, leakage,erosion, sand, strain and production fluid content and composition. Inaddition, sensors may be provided to measure motor current and voltageof the electric actuators, and vibration and displacement or rotation oftheir associated valves.

By way of example, a vibration sensor may be provided for detectingvibration in a flowline. Pressure and temperature sensors may beprovided for monitoring the production fluid. One or more leak detectionsensors may be provided for monitoring integrity of certain connections.Erosion and/or corrosion sensors may be provided in the flow loops.Valve position sensors, choke position sensors, and ROV panel positionindicators may be provided for monitoring the actual valve positions.Shear pin failure sensors may be provided for monitoring the hydraulicactuators and linear overrides. Other various component sensors may alsobe provided for monitoring parameters such as motor voltage, motorcurrent, pump characteristics, etc.

Also, multiple sensors may be provided for measuring a particularparameter at a given location or component. For example, multiplevoltage and current sensors may be provided to allow measurement ofparticular electric motor performance as well as voltage or currentsurges, spikes, etc. The duplicate sensors provide both built inredundancy and a means for cross-checking sensor performance.

In another embodiment multiple wireless base units may be deployed on ornear the christmas tree or subsea processing system to access themultitude of sensors. In this embodiment each base unit may beconfigured to communicate with a corresponding set of sensors.

As an alternative to radio frequency communications, the subsea wirelessmonitoring and control system of the present invention may employmagnetic or optical signals. In any case, however, the transmitters willpreferably generate and detect digitally modulated signals.

In another embodiment of the invention, the wireless monitoring andcontrol system may include conventional means to compress the sensordata prior to transmission so that a lower carrier frequency, which willhave a lower attenuation in water, may be employed. This will alloweither greater ranges to be used or the power requirements for thewireless systems to be reduced.

It should be recognized that, while the present invention has beendescribed in relation to the preferred embodiments thereof, thoseskilled in the art may develop a wide variation of structural andoperational details without departing from the principles of theinvention. Therefore, the appended claims are to be construed to coverall equivalents falling within the true scope and spirit of theinvention.

What is claimed is:
 1. A method for monitoring a subsea hydrocarbonproduction or processing apparatus, the method comprising: mounting asubsea control module (SCM) on or adjacent the apparatus; mounting afirst base unit on or adjacent the apparatus at a distance from the SCM;mounting a plurality of first sensor devices on the apparatus, each ofthe plurality of first sensor devices being configured to generate afirst sensor signal representative of a condition of a component of theapparatus or a property of a fluid in the apparatus; operating eachfirst sensor device to generate a corresponding first sensor signal;wirelessly transmitting each first sensor signal from its correspondingfirst sensor device to the first base unit; wirelessly receiving thefirst sensor signals at the first base unit; transmitting the firstsensor signals from the first base unit to the SCM; and receiving thefirst sensor signals at the SCM; whereby the SCM is provided with aplurality of first sensor signals which are representative of acondition of each of a number of first components of the apparatusand/or a property of a fluid at each of a number of first locations inthe apparatus.
 2. The method of claim 1, further comprising: operatingat least one of the SCM and the first base unit to generate a firstcommand signal; wirelessly transmitting the first command signal fromthe first base unit to the first sensor devices; and wirelesslyreceiving the first command signal at each first sensor device; whereineach first sensor device wirelessly transmits its corresponding firstsensor signal to the first base unit in response to the first sensordevice receiving the first command signal.
 3. The method of claim 2,wherein the first command signal is transmitted from the first base unitto each first sensor device simultaneously.
 4. The method of claim 2,further comprising: after the step of operating each first sensor deviceto generate a corresponding first sensor signal, and prior to the stepof receiving the first command signal at each first sensor device,storing each first sensor signal at its corresponding first sensordevice.
 5. The method of claim 4, further comprising: after the step ofwirelessly receiving the first sensor signals at the first base unit,and prior to the step of transmitting the first sensor signals from thefirst base unit to the SCM, storing the first sensor signals at thefirst base unit.
 6. The method of claim 1, further comprising: after thestep of wirelessly receiving the first sensor signals at the first baseunit, and prior to the step of transmitting the first sensor signalsfrom the first base unit to the SCM, storing the first sensor signals atthe first base unit.
 7. The method of claim 1, further comprising:mounting a second base unit on or adjacent the apparatus at a distancefrom both the SCM and the first base unit; mounting a plurality ofsecond sensor devices on the apparatus, each of the plurality of secondsensor devices being configured to generate a second sensor signalrepresentative of a condition of a component of the apparatus or aproperty of a fluid in the apparatus; operating each second sensordevice to generate a corresponding second sensor signal; wirelesslytransmitting each second sensor signal from its corresponding secondsensor device to the second base unit; wirelessly receiving the secondsensor signals at the second base unit; transmitting the second sensorsignals from the second base unit to the SCM; and receiving the secondsensor signals at the SCM; whereby the SCM is provided with a pluralityof second sensor signals which are representative of a condition of eachof a number of second components of the apparatus and/or a property of afluid at each of a number of second locations in the apparatus.
 8. Themethod of claim 7, further comprising: operating at least one of the SCMand the first base unit to generate a first command signal; operating atleast one of the SCM and the second base unit to generate a secondcommand signal; wirelessly transmitting the first command signal fromthe first base unit to the first sensor devices; wirelessly transmittingthe second command signal from the second base unit to the second sensordevices; wirelessly receiving the first command signal at each firstsensor device; and wirelessly receiving the second command signal ateach second sensor device; wherein each first sensor device wirelesslytransmits its corresponding first sensor signal to the first base unitin response to the first sensor device receiving the first commandsignal; and wherein each second sensor device wirelessly transmits itscorresponding second sensor signal to the second base unit in responseto the second sensor device receiving the second command signal.
 9. Themethod of claim 8, wherein the first command signal is transmitted fromthe first base unit to the first sensor devices simultaneously and thesecond command signal is transmitted from the second base unit to thesecond sensor devices simultaneously.
 10. The method of claim 8, furthercomprising: after the step of operating each first sensor device togenerate a corresponding first sensor signal, and prior to the step ofreceiving the first command signal at each first sensor device, storingeach first sensor signal at its corresponding first sensor device; andafter the step of operating each second sensor device to generate acorresponding second sensor signal, and prior to the step of receivingthe second command signal at each second sensor device, storing eachsecond sensor signal at its corresponding second sensor device.
 11. Themethod of claim 10, further comprising: after the step of wirelesslyreceiving the first sensor signals at the first base unit, and prior tothe step of transmitting the first sensor signals from the first baseunit to the SCM, storing the first sensor signals at the first baseunit; and after the step of wirelessly receiving the second sensorsignals at the second base unit, and prior to the step of transmittingthe second sensor signals from the second base unit to the SCM, storingthe second sensor signals at the second base unit.
 12. The method ofclaim 7, further comprising: after the step of wirelessly receiving thefirst sensor signals at the first base unit, and prior to the step oftransmitting the first sensor signals from the first base unit to theSCM, storing the first sensor signals at the first base unit; and afterthe step of wirelessly receiving the second sensor signals at the secondbase unit, and prior to the step of transmitting the second sensorsignals from the second base unit to the SCM, storing the second sensorsignals at the second base unit.